The present invention relates to elevator systems, and more particularly to tension members for such elevator systems.
A conventional traction elevator system includes a car, a counterweight, two or more ropes interconnecting the car and counterweight, a traction sheave to move the ropes, and a machine to rotate the traction sheave. The ropes are formed from laid or twisted steel wire and the sheave is formed from cast iron. The machine may be either a geared or gearless machine. A geared machine permits the use of higher speed motor, which is more compact and less costly, but requires additional maintenance and space.
Although conventional round steel ropes and cast iron sheaves have proven very reliable and cost effective, there are limitations on their use. One such limitation is the traction forces between the ropes and the sheave. These traction forces may be enhanced by increasing the wrap angle of the ropes or by undercutting the grooves in the sheave. Both techniques reduce the durability of the ropes, however, as a result of the increased wear (wrap angle) or the increased rope pressure (undercutting). Another method to increase the traction forces is to use liners formed from a synthetic material in the grooves of the sheave. The liners increase the coefficient of friction between the ropes and sheave while at the same time minimizing the wear of the ropes and sheave.
Another limitation on the use of round steel ropes is the flexibility and fatigue characteristics of round steel wire ropes. Elevator safety codes today require that each steel rope have a minimum diameter d (dmin=8 mm for CEN; dmin=9.5 mm (xe2x85x9cxe2x80x3) for ANSI) and that the D/d ratio for traction elevators be greater than or equal to forty (D/dxe2x89xa740), where D is the diameter of the sheave. This results in the diameter D for the sheave being at least 320 mm (380 mm for ANSI). The larger the sheave diameter D, the greater torque required from the machine to drive the elevator system.
Another drawback of conventional round ropes is that the higher the rope pressure, the shorter the life of the rope. Rope pressure (Prope) is generated as the rope travels over the sheave and is directly proportional to the tension (F) in the rope and inversely proportional to the sheave diameter D and the rope diameter d (Prope≈F/(Dd). In addition, the shape of the sheave grooves, including such traction enhancing techniques as undercutting the sheave grooves, further increases the maximum rope pressure to which the rope is subjected.
The above art notwithstanding, scientists and engineers under the direction of Applicants"" Assignee are working to develop more efficient and durable methods and apparatus to drive elevator systems.
According to the present invention, a tension member for an elevator has an aspect ratio of greater than one, where aspect ratio is defined as the ratio of tension member width w to thickness t (Aspect Ratio=w/t).
A principal feature of the present invention is the flatness of the tension member. The increase in aspect ratio results in a tension member that has an engagement surface, defined by the width dimension, that is optimized to distribute the rope pressure. Therefore, the maximum pressure is minimized within the tension member. In addition, by increasing the aspect ratio relative to a round rope, which has an aspect ratio equal to one, the thickness of the tension member may be reduced while maintaining a constant cross-sectional area of the tension member.
According further to the present invention, the tension member includes a plurality of individual load carrying cords, strands and/or wires encased within a common layer of coating. The coating layer separates the individual cords, strands and/or wires and defines an engagement surface for engaging a traction sheave.
Due to the configuration of the tension member, the rope pressure may be distributed more uniformly throughout the tension member. As a result, the maximum rope pressure is significantly reduced as compared to a conventionally roped elevator having a similar load carrying capacity. Furthermore, the effective rope diameter xe2x80x98dxe2x80x99 (measured in the bending direction) is reduced for the equivalent load bearing capacity. Therefore, smaller values for the sheave diameter xe2x80x98Dxe2x80x99 may be attained without a reduction in the D/d ratio. In addition, minimizing the diameter D of the sheave permits the use of less costly, more compact, high speed motors as the drive machine without the need for a gearbox.
The cords, strands and/or wires in the tension member of the invention are preferably steel and organic fiber in a number of combinations. The two materials may be maintained separately and comprise distinct steel cords and organic fiber cords in the common jacket; the two materials may be combined into a single cord, a plurality of which cords are dispersed in the common jacket; the materials may be wrapped one around the other in ordered arrays within the common jacket; and the organic fibers may be randomly dispersed in the common jacket with steel cords being also dispersed therein.
Each of the combinations noted provides a hybrid flexible flat tension member having strengths and advantages not available in steel cord flat tension members or organic fiber flat tension members. Advantages of each material individually include for steel: nondestructive examination capabilities; high heat resistance; low stretch. And for organic fiber: low weight and high strength; not susceptible to corrosion. Creating a tension member that effectively employs both steel and organic fibers where load is shared between the two provides a tension member having significantly enhanced properties. The present invention provides several embodiments which allow the two materials to xe2x80x9cshare-the-loadxe2x80x9d which requires consideration of load carrying capability of each of the types of material; the long term bending fatigue resistance of the individual materials; the stretch of each material and belt tracking stability achieve such synergistic benefits.